1. Technical Field
The present invention relates to a semiconductor device and a method for manufacturing thereof.
2. Related Art
Japanese Patent Laid-Open No. 2005-167,198 discloses a semiconductor device, which is provided with a seal ring. The seal ring is composed of a plurality of stacked electroconducting plugs. These electroconducting plugs are formed simultaneously with forming the contact plug in a region for forming an electric circuit. Further, these electroconducting plugs are so-called trench contacts, and continually surrounding a region for forming an electric circuit. Such seal ring allows inhibiting a water influx into the region for forming the electric circuit from the exterior thereof.
Other prior art literatures related to the present invention includes Japanese Patent Laid-Open No. 2006-147,668, in addition to the aforementioned Japanese Patent Laid-Open No. 2005-167,198.
Nevertheless, in a case of employing a seal ring that continually surrounds a region for forming an electric circuit, a space of an opening constituting an electroconducting plug is considerably larger than a space of an opening for forming a contact plug. Therefore, concerning an etch rate for forming both openings by etch processes, an etch rate for the opening for the above-described electroconducting plug is lower than an etch rate for the opening for the contact plug. Therefore, an excessive etching occurs in a section where the opening for contact plug is formed, causing a damage to a diffusion layer located under the opening. When a dynamic random access memory (DRAM) is provided in the region for forming electric circuits, a damage in the diffusion layer induces an increased cell leakage current, deteriorating data-storing ability of the DRAM.